HPC of South Bend and St. Joseph County - Standards Update Draft

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City of South Bend and St. Joseph County Historic Preservation Guidelines 105 For More Information: Masonry Matching Historic Mortar —Most pre-mixed mortar available from hardware stores is generally inappropriate for historic masonry as it contains too much Portland cement and is too hard . The most exact method of matching historic mortar is to have it analyzed by a professional lab . Masonry Cleaning Appropriate masonry cleaning can enhance the character and overall appearance of a building . However, improper cleaning of historic masonry can damage historic surfaces and cause more harm than good both physically and visually . Masonry cleaning methods fall within three general categories: • Low pressure water, with the possible use of gentle detergent and brushing with a natural bristle brush . • Mechanical cleaning including sandblasting, power washing, grinding, sanding and wire brushing . • Chemical cleaning . Because of the potential damage to historic surfaces, cleaning should be completed only when necessary using the gentlest means possible . In many cases, soaking the masonry with low pressure water can remove much of the surface dirt and deposits . If the soaking method is not successful, it might be necessary to add a non-ionic detergent, such as dish washing detergent, or brush the wall surface with a natural bristle brush . The use of mechanical methods, including abrasive blasting, power washing, sanding, or grinding, will remove decorative details and the protective surface of the masonry, resulting in an eroded surface and permanent damage . Abrasively cleaned masonry usually has a rougher surface that can hold additional dirt and be more difficult to clean in the future. Chemical cleaners can etch, stain, bleach or erode masonry surfaces . Both mechanical and chemical cleaning methods can destroy the protective layer, making the masonry surfaces more porous and deteriorate mortar joints, allowing for increased moisture penetration and acceleration of deterioration . In instances where a severe stain or graffiti is present, it might be necessary to use a chemical cleaner in specific areas. Caution should be taken to test the effects of the proposed cleaner on a discrete area of the building before using it on a principle elevation. It is recommended that the most diluted possible concentration be used to minimize potential damage of the masonry surface . It should be noted that many chemical cleaners are hazardous and require special handling, collecting and appropriate disposal of the chemicals and rinse water . Masonry Coatings Water repellent and waterproof coatings are generally applied to prevent water from entering a masonry wall but tend to be unnecessary on weather-tight historic buildings and problematic long term. Water infiltration through masonry buildings is often caused by other moisture related problems including open mortar joints and poor or differed maintenance. In instances where the surface of the masonry has been severely compromised, such as sandblasted brick, the use of water repellent coatings might be appropriate . Water Repellent Coatings, also referred to as “breathable” coatings, keep liquid from penetrating a surface but allow water vapor to escape . Many water repellent coatings are transparent or clear when applied but might darken or discolor over time . Waterproof Coatings seal surfaces and prevent water and vapor from permeating the surface . Generally, waterproof coatings are opaque or pigmented and some include bituminous coatings and some elastomeric coatings and paint . Waterproof coatings can trap moisture inside of a wall and can intensify damage . Trapped moisture can freeze, expand, and spall masonry surfaces . Return to the Table of ContentsDRAFT